The present invention relates to a method and a device for frequency analysis of data. It is applicable in particular to the analysis of test data for expanding the flight envelope of airplanes.
The present invention is applicable in particular, within the aeronautical sector, to flight commands, for example, the analysis and control of vibrational modes of the structure during flight, within the automobile sector, to studies and controls of vehicle vibrations, in electrodynamics (control of electricity-generating machines), especially in the nuclear sector, to vibrational monitoring of the reactor core, in mechanics (study and control of moving parts), in seismics (study of signals used in oil exploration) and in zoology (study of sounds emitted by animals).
The objective of the present invention is to estimate, in the course of testing (during flight in the case of an airplane), the characteristics of the vehicle and in particular the resonance frequencies and the spectral characteristics. In other words, this involves extracting, from the very large quantity of information items originating from transducers installed in the vehicle, the pertinent signatures very rapidly, even in real time.
The set of characteristics of the system determined in this way permits the designers to improve the structure of the system with a view to increasing its comfort, its flight envelope, its consumption, etc.
The signals that we wish to analyze are composed of noise, to which there is or are added one or more sinusoidal signals, whose frequencies and amplitudes are capable of varying in the course of time. This involves estimating these frequencies and these amplitudes in real time.
Within the field of aeroelasticity, a discipline studying the interactions between the aerodynamics, the inertial and elastic forces, the phenomenon of flutter is a very dangerous oscillatory instability of the airplane structure (wing unit, fuselage, tailplane, etc.), since it is capable of affecting the integrity of this structure by damaging it as far as rupture. It is a combination of two or more movements, of different nature, of the airplane structure, which movements, together with the appropriate phase differences, permit aerodynamic forces to input energy into the system. The stable phenomenon is then transformed into an unstable phenomenon in which the energy is no longer dissipated: this is mode coupling. The most commonly cited example is flutter of the wing unit resulting from coupling between the bending and torsion modes, which in phase quadrature lead to aerodynamic lift forces in the same direction as the displacement and in this way to divergent oscillations.
Several parameters have an influence in characterization of flutter: the mass, the stiffness, the shape of the structure, as well as the operational conditions, such as speed. In order to guard against this phenomenon, the aircraft manufacturers must study it and, it if exists, demonstrate that its occurrence threshold is situated above the maximum operating speed (plus 15%). Wind-tunnel tests are conducted first of all, supplemented by vibration tests of the airplane structure on the ground. Theoretical studies then make it possible to define a flutter-free zone, from which full expansion of the flight envelope will be possible incrementally by “exciting” the airplane structure.
Methods of identifying modal parameters are used to extract, in quasi-real time, the values of frequency and damping and to study their evolution in the flight envelope. Analysis of temporal data obtained from flutter tests is complex: the data are obscured by noise and must be shaped by signal processing (especially filtering and sub-sampling). Numerous transducers are now used to extract the modal parameters of the aero-elastic structure “globally” and automatically.
The known document WO 03005229 describes a system for frequency analysis of signals emitted by a transducer. However, the resolution of this analysis is limited.
The present invention aims to remedy these disadvantages.